//设置cookie
//exdays是指天数，1
function setCookie(cname, cvalue, exdays) {
	var d = new Date();
	d.setTime(d.getTime() + (exdays * 24 * 60 * 60 * 1000));
	var expires = "expires=" + d.toUTCString();
	document.cookie = cname + "=" + escape(cvalue) + "; " + expires;
}

//获取cookie， unescape
function getCookie(cname) {
	var name = cname + "=";
	var ca = document.cookie.split(';');
	for(var i = 0; i < ca.length; i++) {
		var c = ca[i];
		while(c.charAt(0) == ' ') c = unescape(c.substring(1));
		if(c.indexOf(name) != -1) return c.substring(name.length, c.length);
	}
	return "";
}

//清除cookie  
function clearCookie(name) {
	setCookie(name, "", -1);
}

//检查cookie
function checkCookie() {
	var user = getCookie("username");
	if(user != "") {
		alert("Welcome again " + user);
	} else {
		user = prompt("Please enter your name:", "");
		if(user != "" && user != null) {
			setCookie("username", user, 365);
		}
	}
}